Color framing videotape recording apparatus and method

ABSTRACT

Automatic color framing for editing in a video tape recorder is provided by associating one of the two possible color frame phases with one of the two possible phase relationships between the off-tape color burst and the incoming video color burst. If this association results in the locking of the video tape recorder to the incorrect color frame, the association of the input color burst phase relationship to the color frame phases is reversed to provide correct color framing in subsequent edits in response to the off-tape to input video color burst phase so long as the input video horizontal sync to color burst phase remains substantially constant.

[ Apr. 15, 1975 COLOR FRAMING VIDEOTAPE RECORDING APPARATUS AND METHODPrimary ExaminerRobert L. Griffin Assistant ExaminerMitchell SaffianAttorney, Agent, or Firm-Limbach, Limbach &

[75] Inventor: Nikola 'Vidovic, Santa Clara, Calif. Sutton [73]Assignee: International Video Corporation,

Sunnyvale, Calif. [57] ABSTRACT [22] Fil d; M i, 15, 1974 Automaticcolor framing for editing in a video tape recorder is provided byassociating one of the two pos- [211 App! 451525 sible color framephases with one of the two possible phase relationships between theoff-tape color burst [52] U.S. Cl. 358/4 and the incoming video color Ifthis association [51] Int. Cl. H04n 5/78 results in the locking of theVideo p recorder to the 58 Field of Search 358/4; l78/6.6 A, 6.6 R,incorrect color frame, the association of the input 178/69 5 TV 695 C13color burst phase relationship to the color frame phases is reversed toprovide correct color framing in sub- 5 References Cited sequent editsin response to the off-tape to input video UNITED STATES PATENTS colorburst phase so long as the input video horizontal 3 735 0'5 5,1973 Mesak358/4 sync to color burst phase remains substantially con- 3176116049/1973 Ozawa et al. 358/4 9 Claims, 17 Drawing Figures 2 PHA6ES 0F COLORFRAME PULSES 15 Hz) 1 420 M0l Cfi0ME ELECTKONIC m LOGIC 270 Piiii' g'gg' SWITCH m FIGURE 9 (FROM FLIP-FLOP 73, FIG. M) L 422 [424 TAPE PHASELOCKED COLOE BURST Loops COLOR FRAME PHASING CIRCUITRY INPUT PHASELOCKED PHASE COLOR o BURST LOOP SHIFTER EDIT LOCK BUS TENIEUAPR 1 5197sSHEET C 1 BF 1 7 CLOCK SIGNAL GENERATOR 2/ Q W' I I r REF. PULSESTRIPPED l 23 PHASE LOCKED LOOP I 36 m PULSE I a 1! AND 1 COMPARE V60 (Kv GATE5 Q AUTOMATIC I I 7 STATION SWITCH/N6 I 'L 4 COMPOSITE L I NC I 37h r v VSTAL I LOCK "f" CONTROLLED DETECTOR 05c. I L CLOCK SIGNAL L 1L fh0%? ?7 I FIEIID r 1%? A9 I RESET FRAME DETECTOR (7 87 105 GENERATURFIELD PULSE +2 SERVO I 69 NORMAL OUTPUTS ,KEsEr I REFER- Q RECORD f NOTADVANCED ENCE c? DIV/DE I 7lx H 58 1 ADVANCE COUNTER {H 42 PLAYBACK l, K2) K HZ EDIT 2H ADVANCE m) LOGIC I RECORD 33 59 I J /77 I M I I I- 1 LNE UP 92 CLOCK ED T l REFERENCE J DMDER K1 TIME BASE CORRECTOR 7MONOCHROME LINE REFERENCE PULSE OUTPUT 95/ E89 FRAME RATE RESET I01 95FIELD REFERENCE OUTPUTS 99 DIVIDER (T0 SERVO) (K2) 98 F I Er 1APATENTEUAPRI 5 @925 SHEEF 07 0F 17 m E H g 22:2: sa 53s SE28 NEE ma mae. 225% 3528 cccccccccccccc E3 5 E 52$ a 7 EEQ 3E2 $5 556 658 $33 EmPATENIEBAPR 1 51.975 3.878557 saw 08 or 17 I I I i Z I I I w L5 2 [1i12X E REFERENCE CONTROL VAR! BLE "A" ?I'PITENTEUAPR I 51975 3, 878,557SHEET 12 Jr '1? HOK/Z. T0 PHASE TACH REF. PULSES ERROR DETECTOR l2 (6KHZ) VOLTAGE CLOCK I I II 309 DELAY w 331 INHIBIT NORMAL "SET RESET FLIPA FLOP TRIGGER 315 V A VOLTAGE INHIBIT NORMAL CDNTROLLED CONTROL ENABLE518 3B CLEAR DIGITAL COMPARATOR COUNTER LATCHES COLOR FRAMING VIDEOTAPERECORDING APPARATUS AND METHOD 1 BACKGROUND OF THE INVENTION The presentinvention relates tov video tape recorders (VTRs) and, moreparticularly, to electronic editing of NTSC color television signals onaVTR. The present invention is useful in all types of high quality VTRs,including both quadruplex and helical scan type VTR's.

In the process of editing tapes on a VTR, either a series of'newsegments are recorded in sequence (assemble" editing) or a new segmentis recorded in a previously recorded segment (insert" editing). Ineither case, the precise timing" of the ultimately recorded sequencemust not vary and particularly the timing at the beginning and end ofsegments must match that of adjacent segments. By timing is meant thephase of the horizontal synchronization pulses of the recorded videosignal. Such requirements are well known in the art.

Typically, in playback modes of VTR operation, the off-tape horizontalpulses are locked to a reference signal (horizontal lock) by means of aphase locked servo arrangement which controls the rotational phase ofthe mechanical scanner member which carries the VTR record/playbackheads.

A problem in editing is that the horizontal lock is obviouslyinoperative during record. A prior art technique is to place the VTR inthe tachometer mode (i.e. the playback timing is not finely controlledby locking the horizontal pulses to a reference, but instead is coarselycontrolled, the scanner tachometer is phase locked to referencetachometer pulses, such tachometer pulses occurring at a slower ratethan the horizontal pulses and such pulses not related to a signalreproduced by the VTR) and manually adjusting the tachometer reference(or equivalent) to secure zero hori- 4 zontal error which is usuallyadequate to assure proper timing in subsequent edit record sequences.This approach requires additional set up time and operator skill.

An automatic means for securing zero horizontal error during edit recordsequences is the subject of US. patent application Ser. No. 356,839 ofBert H. Dann, filed May 3, 1973, now abandoned, entitled VideotapeRecorder Editing Apparatus. According to the teachings of thatapplication, the horizontal error during edit playback is stored toprovide the same error correction during edit record sequences therebymaintaining the same timing throughout the recorded material.

Nevertheless, a further problem occurs in the editing of colortelevision signals. In order to fully appreciate this problem one mustconsider not only the nature of the color television signal itself butalso the action of time base correctors which are almost universallyemployed in high quality VTRs, particularly VTRs used in broadcasting.These problems are discussed in an article The Problems of Splicing andEditing Color Video Magnetic Tape by C. A. Anderson in the IEEETransactions on Broadcasting, Vol. BC-IS, No. 3, September, I969.

First, with regard to the color television signal itself, there are twopoints to consider. With respect to a par ticular video source, a colorframe is two monochrome frames. That is, because the NTSC colorburstshifts phase each frame, it is two frames before 1 the same phaseis repeated. Also, the phase of the color burst with respect to thehorizontal sync pulse is not defined. While this phase relation willtypically be stable as to a particular video source, it will not be thesame in different video sources. It will therefore be apparent that thecolor frame is not uniquely defined in any manner.

Second, with regard to time base correctors, a typical correction schemein a color VTR includes two variable delay lines in series to removeresidual time base errors still present despite a horizontal locking ofthe VTR servo systems. The first delay line is controlled by an errorsignal derived by comparison of off-tape to the input video horizontalsync pulses. The input video signal is the signal which is to be editedinto material previously recorded on the tape. In most circumstances theinput video signal will have a highly stable horizontal sync and colorburst and the phase relation between sync and burst, whatever it may be,remains stable. The second delay line provides a fine correction underthe control of an error signal comparing off-tape burst to a subcarrierderived from the input video signal. As will be explained, it is thislast correction that causes color editing problems.

As part of the VTR lock-up sequence, the VTR synchronizes the off-tapemonochrome frame to the input video monochrome frame. Because there isno way to identify the color frame the machine has a fiftyfifty chanceof locking to the correct color frame. In either case, the VTR proceedsto achieve horizontal lock to the input video signal. Thus, thehorizontal sync pulses are closely in phase at the output of the machineand even more closely in phase at the output of the first delay line inthe time base corrector. However, prior to the second delay line, thephase difference between the reference subcarrier and the off-tape colorburst is either 9 or 9 180 depending on which phase of the color framethe VTR happened to lock to. The phase angle 6 indicates the differencein phase between the input video color burst and the off-tape colorburst due to the undefined phase relationship between the horizontalsync and color burst of any NTSC color television signal. In eithercase, the second delay line will resolve the phase difference 9 or O180.

However, at an edit point, if the second delay line suddenly must changefrom resolving a 9 to a 9 180 error or vice-versa there is an abrupt 180shift. Such a shift is equivalent to I40 nanoseconds of delay andresults in a disturbing and noticeable sideways jump in the reproducedpicture from the VTR. This effect is particularly disturbing inanimation.

SUMMARY OF THE INVENTION sync and burst derived from a single stablegenerator) the phase of the horizontal sync to burst in the input videosignal and in the off-tape video signal will each remain constant.However, the relative phase of the off-tape burst and input video burstwill either be 9 or O 180 depending on which phase of the color framethat the VTR happens to lock to. By comparing the input color burst tothe off-tape color burst the relative phase relation of those two burstscan be stored. Then, for example, a test edit can be made to provide avisual determination if the VTR locked to the wrong color .FIGS. 6A-Nare a series of waveforms useful in understandingFIG. 4.

FIG. 7 is a timing diagram useful in understanding FIG. 4.

frame Phase y looking for a de ays jump in the re- FIG. 8 is a blockdiagram of a scanner servo system produced picture at the edit point.Circuitry is then of a video tape recorder particularly adapted for useprogrammed to select the correct phase of the color with the presentinvention. frame by comparing the relative off-tape to input video FIG 9i a block diagram of a capstan servo system color burst phases. For theparticular input video signal f a vid o t e recorder particularlyadapted for use source and off-tape video signal the relative burstphase 10 with the present invention. requires a selection of aparticular color frame phase. FIG. 10 is a block diagram of oneembodiment of the Having found that relationship the VTR will automatiot llabl delay of FIG. 8. cally lock o h rr c l r fr m p n p r g FIG. 11is a block diagram of the digital delay portion the two color burstphases. The VTR may even be f FIG 10, turned off and days or weeks maypass once this rela- P10. 12 is a block diagram of an alternativeemboditionship is initially determined and automatic lock to ment of thecontrollable delay of FIG. 8. the correct frame will still occur so longas the horizon- FIG 13 i a blo k diagram of the A/D and D/A portal syncto color burst phase of the input video signal io f FIG 12, (1068 notChange n i y. FIG. 14 is a block diagram of a time base corrector Theseand other advantages and features of the inte the operation of which isuseful to an undervention will be recognized more fully as the detailedstanding of the present invention. description of the preferredembodiments, claims and FIG 15 is a block diagram of one embodiment ofthe accompanying drawings are read and understood. i v ti n,

FIG. 16 is a more detailed block diagram of an em- BRIEF DESCRIPTION OFTHE DRAWINGS bodimem of the invention FIG. 1 is a system block/diagramof an input synchro- HA4.) a 5.61165 of waveforms useful m understandingthe invention. mzlng signal processor particularly adapted for use withthe present invention. DESCRIPTION OF THE PREFERRED FIG. 2 is a blockdiagram showing use of the input EMBODIMENTS Synchronizing signalProcessor 1 in edit m In order to completely understand the presentinven- 3 15 a block diagram showmg an alternanve tion, various detailsof an exemplary VTR are disclosed of n for the purposes of a completedisclosure. It will be un- Q- 4 IS a general block diagram 9 themlscount derstood that the invention is not limited to the contextPhasing System useful understanding the Servo 3 of the particular VTR ofwhich portions are herein detems particularly adapted for use with thepresent lnscribed. The overall exemplary VTR is described in vention.greater detail in the following copending applications FIG. 5 is a blockdiagram of the logic block of FIG. and patents, assigned to the presentassignee, all of 40 which are incorporated herewith by reference:

Patent No. Title Issued Inventor(s) 3,783,398 FM PULSE AVERAGING 1- 1-74Bert H. Dann DEMODULATOR 3,809,809 TECHNIQUE FOR DETECT- 5- 7-74 NikolaVidovic ING LONG DURATION PULSES FROM A TRAIN OF SHORT DURATION PULSES3,862,355 HELICAL SCAN WIDEBAND 1-21-75 Barett E.

TAPE RECORDER APPARA- Guisinger TUS AND METHOD 3,852,617 PASSIVE PEAK12- 3-74 Nikola Vidovic DETECTOR AND LEVEL SHIFTER 3,843,957 VIDEOPROCESSING 10-22-74 Nikola Vidovic CURCUIT 3,806,794 PHASE SHIFTER4-23-74 Nikola Vidovic APPARATUS Application Ser. No. Title FiledInventor(s) 285,919 SYNCHRONIZING PULSE 9- l-72 Bert H. Dann andPROCESSOR FOR A Nikola Vidovic VIDEO TAPE RECORDER 285,917 VIDEO TAPERECORDER 9- 1-72 Kenneth Louth METHOD AND APPARATUS 354,227 MAGNETICTAPE 4-25-73 Frank S. C. MO and TRANSPORT SYSTEM Vernon Natwick 355,220VIDEOTAPE RECORDER 4-27-73 Barrett E.

AND REPRODUCER Guisinger and VELOCITY COMPENSATOR Bert H. Dann APPARATUS356,380 VIDEO TAPE RECORDER 5- 2-73 Kenneth Louth METHOD AND APPARATUS

1. A method for providing automatic color framing in a video taperecorder wherein incoming color video signals having substantiallystable horizontal sync to color burst phase are edit recorded adjacentpreviously recorded color video signals having a substantially stablehorizontal sync to color burst phase, said video tape recorder includingmeans for synchronizing in one of two possible phase relationships asignal at the color frame rate of the previously recorded color videosignals with a reference signal at the color frame rate derived from theincoming color video signals, the method comprising comparing the phaserelation of the color burst of the incoming color video signals to thecolor burst of the reproduced previously recorded color video signals todefine said phase relation as the first phase relation to associate saidfirst phase relation with synchronization in one of said two possiblephase relationships of said signal at the color frame rate of thepreviously recorded color video signals and said reference signal at thecolor frame rate derived from the incoming color video signals, and todefine a 180* shifted phase relation of said color bursts as the secondphase relation to associate said second phase relation withsynchronization in the other of said two possible phase relationships ofsaid signal at the color frame rate of the previously recorded colorvideo signals, edit recording said incoming color video signals adjacentsaid previously recorded color video signals, reproducing saidpreviously recorded color video signals and said newly edited recordedincoming color video signals, reversing the association of said firstand second phase relations of said color bursts to said possible phaserelationships of said signal at the color frame rate of the previouslyrecorded color video signals and said reference signal at the colorframe rate derived from the incoming color video signals when thereproduced previously recorded color video signals and said newly editedrecorded color video signals have a 180* color burst phase shift at theedit point whereby the comparison of the phase relation of the colorburst of the incoming color video signals to the color burst of thereproduced color video signals to determine if said phase relation issubstantially said first or substantially said second phase relationcauses synchronization in the associated one of said two possible phaserelationships of said signal at the color frame rate of the previouslyrecorded color video signals and said reference signal at the colorframe rate derived from the incoming color video signals.
 2. The methodof claim 1 wherein said step of comparing the phase relation of thecolor burst of the incoming color video signals to the color burst ofthe reproduced previously recorded color video signals includes thesteps of generating a first stable color subcarrier signal in responseto said color burst of the incoming color video signals, generating asecond stable color subcarrier signal in response to said color burst ofthe reproduced previously recorded color video signals, and comparingthe phase relation of said first and second stable color subcarriersignals.
 3. In a video tape recorder wherein incoming color videosignals having substantially stable horizontal sync to color burst phaseare edit recorded adjacent previously recorded color video signalshaving a substantially stable horizontal sync to color burst phase, saidvideo tape recorder including means for synchronizing in one of twopossible phase relationships a signal at the color frame rate of thepreviously recorded color video signals with a reference signal at thecolor frame rate derived from the incoming color video signals, colorframing apparatus comprising means for comparing the phase relation ofthe color burst of the incoming color video signals to the color burstof the reproduced previously recorded color video signals to generate afirst signal when said phase relation is and to generate a second signalwhen said phase relations is Theta + 180*, means for applying said firstand second signals to said means for synchronizing to synchronize saidcolor frame rate signals in a first phase relationship in response tosaid first signal and to synchronize said color frame rate signals in asecond phase relationship in response to said second signal, and meansfor reversing said first and second signals.
 4. The combination of claim3 wherein said means for comparing the phase relation of said colorbursts includes means for generating a first stable color subcarrier inresponse to said color burst of the input color video signals, means forgenerating a second stable color subcarrier signal in response to saidcolor burst of the reproduced previously recorded color video signals,and means for comparing the phase relation of said first and secondstable color subcarrier signals.
 5. The combination of claim 4 whereinsaid means for comparing the phase relation of said first and secondstable color subcarrier signals comprises means for adding said firstand second stable subcarrier signals, and means for detecting therelative amplitude of said added first and second stable subcarriersignals to detect the relative phase of said subcarrier signals.
 6. Thecombination of claim 5 wherein said means for reversing said first andsecond signals comprises means for shifting the phase of one of saidsubcarrier signals.
 7. In a video tape recorder wherein incoming colorvideo signals having substantially stable horizontal sync to color burstphase are edit recorded adjacent previously recorded color video signalshaving a substantially stable horizontal sync to color burst phase, saidvideo tape recorder including means for synchronizing in one of twopossible phase relationships a signal at the color frame rate of thepreviously recorded color video signals with a reference signal at thecolor frame rate derived from the incoming color video signals, therelative phase of the incoming video signals'' color burst to thepreviously recorded video signals'' color burst defining the correctphase relationship of said color frame rate signals, color framingapparatus comprising means for comparing the phase relation of the colorburst of the incoming color video signals to the color burst of thereproduced previously recorded color video signals to generate a firstsignal when said phase relation is Theta * and to generate a secondsignal when said phase relation is Theta + 180*, and means for applyingsaid first and second signals to said means for synchronizing tosynchronize said color frame rate signals in a first phase relationshipin response to said first signal and to synchronize said color framerate signals in a second phase relationship in response to said secondsignal.
 8. The combination of claim 7 wherein said means for comparingthe phase relation of said color bursts includes means for generating afirst stable color subcarrier in response to said color burst of theinput color video signals, means for generating a second stable colorsubcarrier signal in response to said color burst of the reproducedpreviously recorded color video signals, and means for comParing thephase relation of said first and second stable color subcarrier signals.9. The combination of claim 8 wherein said means for comparing the phaserelation of said first and second stable color subcarrier signalscomprises means for adding said first and second stable subcarriersignals, and means for detecting the relative amplitude of said addedfirst and second stable subcarrier signals to detect the relative phaseof said subcarrier signals.